CospasCospas--Sarsat Sarsat --Satellite SAR ... Location katz.pdf · Daniel Katz © Mobit Telecom...
Transcript of CospasCospas--Sarsat Sarsat --Satellite SAR ... Location katz.pdf · Daniel Katz © Mobit Telecom...
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SAR SAR –– LocationLocation
Founded in 1982 by Canada, France, Russia, USA
43 countries and organizations participate (2010)
Instrumental in the Instrumental in the rescue of >rescue of >3030,,000 000 liveslives
No end user fees
Israel is not a member but uses C/S – ships, yachts, airplanes
CospasCospas--Sarsat Sarsat -- Satellite SAR SystemSatellite SAR System
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Provide accurate, timely, and reliable distress alert and location data to help SAR authorities assist persons in distress
Mission of C/S
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System Structure
77 Ground stations (LUTs) receive, process and forward satellite downlinks.
Radio beacons: EPIRBs - ships, ELTs - airplanes, PLBs – personal.
Satellites - relay distress signals to ground stations.
30 Mission Control Centers (MCCs) distribute alerts to RCCs, SPOCs or
other MCCs.
Rescue Coordination Centers (RCCs), ~1 per country, coordinate the actual
SAR activity.
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SAR SAR –– LocationLocation
GEOLUT & LEOLUT at ITMCC
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Radio beacons
EPIRBs (Emergency Position Indicating Radio Beacons) – for maritime use.
ELTs (Emergency Locator Transmitters) – for aircraft.
PLBs (Personal Locator Beacons) - for personal use.
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Wrist Worn PLB – SAT406 (by Mobit)
Ensuring availability when the unexpected occurs
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SAR Satellite Constellations
SATs Coverage Availability Latency Accuracy Method
LEOSAR 6 Full ~ every 1h Up to ~1h ~1500m Doppler
GEOSAR 5 70°S-70°N Always Immediate ~125m* GPS
MEOSARMEOSAR >>7575 FullFull AlwaysAlways 2 2 secsec ~~150150mm InverseInverse--GPSGPS
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LEOSAR Location – Satellite Based Location Born
Sputnik - October 4, 1957At a known location (Johns Hopkins Applied Physics Lab - APL)
measuring Doppler shift of Sputnik’s radio signals → Sputnik’s orbit determined.
Frank McClure (APL chairman) suggested that: knowing the satellite's position and
measuring the Doppler shift, → determine location of a receiver on Earth.
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LEOSAR Location – Method: Doppler Effect
∆f/f= Vrel*cos(A1)/C (for stationary beacon Vrel = Vsat)
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Convergence towards the true position
Convergence towards the mirror position
LEOSAR Location – Frequency & Satellite Ground Track
At TCA (Time of Closest Approach) A1=90° and ∆f=0
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Fc
FmF
T
Doppler curve
Fr
• Assume distance [d] from beacon to satellite track
• Generate frequency vs. time curve
• Calculate SQRT [ Σni=1( Fr
i – Fci)2 /n]
• Iterate [d] until the above square root is small enough
LEOSAR Location – Numeric Process
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12
2B
1B2A1A
LEOSAR Location – Solving Ambiguity
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LEOSAR Location – weakness
Small footprint x 6 satellites → Temporal Availability ~1h
Small footprint → Latency (store & forward over the ocean)
Doppler → Depends on Freq. accuracy → Location Accuracy → ~1500m
∆f/f= V*cos(A1)/C
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GEOSAR Location – Geo Sats + GPS Era
GEOSAR Satellite(s)Navigation
Satellites (GPS)
Ground Station Beacon reports GPS position
GEOSAR Satellites + GPS = Worldwide Coverage
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GEOSAR Location – weakness
Stationary Satellites → No Doppler → Dependent on GPS
Short Message → Location report resolution limited to 4” Lat/Lon → ~125m
Far satellites → Lower SNR
GPS orbit inclination 55º → Lower coverage at NZ
No service by the Poles
Far satellites → Lower SNR
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MEOSAR Location – Following the GPS
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MEOSAR Location – weakness (?)
Trilateration Ranging → DSSS transmission → CDMA
Limited BW DSSS → Limited Accuracy → ~150m
1-G (LEOSAR/GEOSAR) Signal BW = 3Khz
2-G (MEOSAR) Signal BW = 60KHz
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Standard Beacon Transmission Time
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Mobit’s method to Communicate Extra Data